Topic 3 – The Periodic Table
Syllabus Statements
• In this topic you will study:
• The Periodic Table
• Physical Properties
• The chemical properties of some elements
and their oxides.
3.1 The Periodic Table
• 3.1.1 Describe the arrangement of elements in the periodic
table in order of increasing atomic number.
• 3.1.2 Distinguish between the terms group and period.
• 3.1.3 Apply the relationship between the electron
arrangement of elements and their position in the table up
to Z=20.
• 3.1.4 Apply the relationship between the number of
electrons in the highest occupied energy level for an
element and its position in the periodic table.
Because I know someone will ask, lets
get this over with straight away
• The trite phrase "the 92 naturally-occurring chemical elements"
is often seen, but is incorrect. There are only 88 naturallyoccurring chemical elements. The elements 43, 61, 85 and 87
have no stable isotopes, and none of long half-life, so they are
not naturally present. Small amounts are made in nuclear
reactions induced by cosmic rays and nuclear tests, but these
soon disappear. If you protest that these should be included,
then so should Np and Pu, which are produced by the absorption
of neutrons arising from spontaneous fission of uranium and
thorium, and then there would be 94 naturally-occurring
elements. If you wait long enough, there will only be 81
naturally-occurring elements, since everything beyond lead has
only unstable isotopes, though some are of very long half-life,
and have survived since the beginning, fathering their
radioactive series. Any way you look at it, there are not just 92
naturally-occurring chemical elements.
• Scientists like to make lists!
• When scientists arranged all the known
elements into order of increasing mass
number, they found patterns in the reactions
of the elements.
• Certain properties seemed to repeat every 8
elements
Atomic number and patterns
reactive gases
H
He
Li
Be B
C
N
O
unreactive gases
F
Ne Na Mg Al
Si
P
S
Cl
reactive metals
Ar
K
• Further study and refinement led to the Periodic
Table, which is one of the most useful tools we
have in chemistry.
• The modern periodic table arranges elements in
order of increasing atomic number.
• Note that we now use the number of protons
NOT the mass number.
• Why?
• The proton number of an element always stays
the same. (Remember isotopes!)
• This order better reflects electronic structure
(why?), which determines the reactions of an
element.
• The periodic table is organised into groups – a
column of the periodic table
• And periods – a row of the periodic table
• Groups and periods can both be numbered
• So we can talk about “the group 7 elements”
• Or “the elements of period 2”
• Note that hydrogen doesn’t really fit into a
group. Sometimes it is placed on its own, and
sometimes it is placed at the start of group 1
Columns of elements
1
2
3
Groups
4
5
6
7
H
Li
He
Be
Ca Sc
Rb Sr
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
Kr
transition elements
Na Mg
K
0
Y
Ti
V
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Cs Ba La Hf Ta W Re Os
Ir
Fr Ra Ac Rf Db Sg Bh Hs Mt
I
Xe
Pt Au Hg Tl Pb Bi Po At Rn
?
?
?
Rows of elements
Periods
1
H
2
Li
Be
B
C
N
O
F
Ne
3
Na Mg
Al
Si
P
S
Cl
Ar
Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
Kr
4
K
He
Ca Sc
Ti
V
5
Rb Sr
6
Cs Ba La Hf Ta W Re Os
7
Fr Ra Ac Rf Db Sg Bh Hs Mt
Y
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Ir
I
Xe
Pt Au Hg Tl Pb Bi Po At Rn
?
?
?
• A few more things to note at IB level:
• Some textbooks (and old doddery teachers like
me) sometimes say group 8 instead of group 0.
They are the same group. Correct me if I get it
wrong!
• Sometimes the transition elements are given
group numbers from 3 to 12.
• Then the old group 3 becomes group 13; the old
group 4 becomes group 14 etc.
• The avoid any confusion the IB textbook refers to
group 3/13; group 4/14 and so on.
• Its easy to understand – it’s just a bit annoying.
Group or Family
Period or Series
The Periodic Table
Group or
family
Period
• Notice that chemists have given some groups
names.
• Group 1 are the alkali metals (why?)
• Group 2 are the alkali earth metals (but these
aren’t studied at IB)
• Group 7 are the halogens
• Group 0 (or group 8) are the noble gases.
• Thinking back to the Atomic Structure topic,
what is the relationship between proton
number and number of electrons?
• They are the same.
• So the periodic table can be used to deduce
the electron structures of all the elements.
• You should already know the first 20.
Element
Lithium
Carbon
Argon
Calcium
Boron
madeupium
doesntexistium
Number of
electrons in
valence shell
Group
number
4
3
Element
Lithium
Carbon
Argon
Calcium
Boron
madeupium
doesntexistium
Number of
electrons in
valence shell
Group
number
1
4
8
2
3
4
3
1
4
8
2
3
4
3
• It should be really really obvious that the
number of electrons an element has in its
outer shell tells us what group the element is
in.
• This applies even to elements you haven’t
heard of (not just the 20 you are supposed to
have learned!)
• How many electrons are in the outer shell of
Gallium, Ga
• It’s in group 3, so it has 3 electrons in its outer
shell
• Less obvious, but still important is the
relationship between the period an element is
in and the number of electron shells it has.
•
•
•
•
Lithium is in period 2
Its electron configuration is 2,1
So it has 2 occupied shells.
2 electrons in the first shell and one electron
in the second shell
• Its highest occupied shell is shell number 2
• Potassium has the electron configuration
2,8,8,1
• It has 4 occupied shells, so it must be in period
4
• Its highest occupied shell is shell 4.
• Note that sometimes we refer to an electron
shell as an “energy level”
Review of syllabus statements
• 3.1.1 Describe the arrangement of elements in the periodic
table in order of increasing atomic number.
• 3.1.2 Distinguish between the terms group and period.
• 3.1.3 Apply the relationship between the electron
arrangement of elements and their position in the table up
to Z=20.
• 3.1.4 Apply the relationship between the number of
electrons in the highest occupied energy level for an
element and its position in the periodic table.